1. Field of the Invention
The present invention is directed to a method for operating a computed tomography apparatus with which a region of a life form, for which a volume dataset of the life form is to be registered, is determined.
2. Description of the Prior Art
Before the definition of the region for which a volume dataset is to be registered, for example by means of a spiral scan, an x-ray shadowgram (topogram) of the life form is usually produced. The definition of the region for which the volume dataset is to be registered ensues by means of a graphic marking of a region, that is generally a rectangular region in the topogram, that includes the region of the life form to be registered. The length of the rectangle defines the length of the spiral scan and the width of the rectangle defines the width of the field of view presented in the CT image.
So that the x-ray topogram covers as few regions as possible that are not allocated to the region to be registered, German PS 42 23 430 teaches that the x-ray topogram be generated keeping pace with the measurement. The x-ray topogram is generated in real time by a computer of the computed tomography apparatus using the output signals of the detector array of the computed tomography apparatus, acquired in real time, to generate an x-ray topogram that corresponds to the degree of the relative position between a measurement unit, including the detector array and the x-ray source, and the patient bed of the computed tomography apparatus.
When the radiation detector has more than one detector array, i.e. when the radiation detector is a matrix detector, it can occur that the matrix detector covers the entire examination region for which the x-ray topogram is to be registered. In this case, the measurement unit formed by the matrix detector and the x-ray source need not move relative to the patient bed. In this context, German OS 197 21 535 discloses a computed tomography apparatus having a matrix detector with which x-ray topograms can be optionally prepared using one or more detector lines. To this end, a tube-proximate slotted diaphragm and a detector-proximate slotted diaphragm are provided. An on-line computing method is employed for the superimposition of the x-ray topograms of the individual detector lines, this including a “deblurring filter” for reduction of the image blurring due to the movement of the patient bed and including correction for stray radiation in the matrix detector.
The marking is manually defined by an operator of the computed tomography apparatus, as a result of which the region for which the volume dataset is to be registered can be relatively imprecisely marked on occasion. The manual setting of this marking is also relatively time-consuming.